A circuit configuration of this type is used, for example, in motor vehicles, to thereby continually have available the instantaneous state of charge of the accumulator battery. By recording the accumulator current, the accumulator voltage and the accumulator temperature, relatively reliable information can be ascertained about the state of the accumulator battery. The indicated quantities are acquired and the state of the accumulator battery is ascertained by the control unit.
Since the control unit is supplied with energy from the accumulator battery, when the engine is at rest and therefore electrical energy is not being produced by the generator installed in a motor vehicle, the control unit discharges the accumulator battery. To prevent this, the control unit is switched off when the motor vehicle is in the rest state. As soon as the ignition is switched off and the current consumption in the motor vehicle has fallen sufficiently, the control unit stores the instantaneous state of the accumulator battery and then switches itself off. The control unit is only switched on again when the ignition is switched on.
Since, however, in today's motor vehicles there are frequently consumers which require energy even in the rest state of the motor vehicle, such as, for example, an ice maker in the trunk of the motor vehicle, current is drawn from the accumulator battery without this being registered by the control unit. Because of this, the state of the accumulator battery ascertained by the control unit no longer agrees with the true state of the accumulator battery.
It may be that it is known from PCT International Patent Publication No. WO 99/50098 to shift a motor vehicle into a rest state (sleep mode) to thereby reduce the energy consumption; however, no indication can be gathered from the cited document to monitor the state of charge of an accumulator battery. The indicated publication deals with a monitoring system of a motor vehicle which has inputs for a plurality of vehicle subsystems. To save on energy, the cited document proposes shifting the motor vehicle into a sleep mode, activation signals (wake-up signals) normally not being given to the inputs of the vehicle subsystems.
During the sleep mode, the inputs are permanently polled to thereby detect the appearance of a wake-up signal. If no wake-up signal appears after a certain time, the cycle time of the polling inputs is increased. If a wake-up signal still does not appear at the inputs after a further predetermined time, the cycle time is increased once more. The intention is to thereby reduce the energy consumption during the sleep mode.
Moreover, German Patent No. 41 23 811 A1 describes a method for operating a microprocessor, in which the microprocessor may be switched from an inactive to an active operating state by an activation signal at an interrupt input. After each entrance into the inactive state, the activation signal is supplied to the interrupt input after a specifiable time.
Furthermore, U.S. Pat. No. 4,965,550 describes a circuit configuration for continually monitoring the status of a plurality of switches and so-called intelligent sensors (smart sensors), which are connected to the switches. Each sensor is connected to a separate single point in a single-wire bus, a smart-sensor multiplex configuration that represents a wake-up circuit acting on the sensor. The wake-up circuit permits the activation of any switch of a group of switches having a high priority, in order to shift a microcontroller automatically from a waiting state into an active state. In the active state, all circuits of the entire system are supplied with energy, whereupon all switches and sensor modules are polled.
It is an object of the present invention to provide a circuit configuration of the type indicated at the outset in such a way that accuracy in recording the state of charge of an accumulator battery is increased.